https://www.jianshu.com/p/8722660782c5 aes加密的文章

IV为偏移量，需要和后台商定

AES加密

+ (NSString *)aesEncrypt:(NSString *)Infotext appSecret:(NSString *)appSecret {
    NSString *method = @"AES-256-CBC";
    NSString *key = [self md5:appSecret];
    NSString *iv = [key substringToIndex:16];
    NSData *ciphertext = [self aesEncrypt:Infotext key:key iv:iv];
    return [self hexStringFromData:ciphertext];
}

+ (NSString *)md5:(NSString *)str {
    const char *cStr = [str UTF8String];
    unsigned char result[CC_MD5_DIGEST_LENGTH];
    CC_MD5(cStr, (CC_LONG)strlen(cStr), result);
    return [NSString stringWithFormat:
            @"%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x",
            result[0], result[1], result[2], result[3],
            result[4], result[5], result[6], result[7],
            result[8], result[9], result[10], result[11],
            result[12], result[13], result[14], result[15]
            ];
}

+ (NSData *)aesEncrypt:(NSString *)data key:(NSString *)key iv:(NSString *)iv {
    NSData *dataBytes = [data dataUsingEncoding:NSUTF8StringEncoding];
    NSData *keyBytes = [key dataUsingEncoding:NSUTF8StringEncoding];
    NSData *ivBytes = [iv dataUsingEncoding:NSUTF8StringEncoding];
    size_t bufferSize = [dataBytes length] + kCCBlockSizeAES128;
    void *buffer = malloc(bufferSize);
    size_t numBytesEncrypted = 0;
    CCCryptorStatus cryptStatus = CCCrypt(kCCEncrypt,
                                          kCCAlgorithmAES128,
                                          kCCOptionPKCS7Padding,
                                          [keyBytes bytes],
                                          kCCKeySizeAES256,
                                         [ivBytes bytes],
                                         [dataBytes bytes],
                                         [dataBytes length],
                                         buffer,
                                         bufferSize,
                                         &numBytesEncrypted);
    if (cryptStatus == kCCSuccess) {
        return [NSData dataWithBytesNoCopy:buffer length:numBytesEncrypted];
    }
    free(buffer);
    return nil;
}

+ (NSString *)hexStringFromData:(NSData *)data {
    Byte *bytes = (Byte *)[data bytes];
    NSString *hexStr = @"";
    for (int i = 0; i < [data length]; i++) {
        NSString *newHexStr = [NSString stringWithFormat:@"%x", bytes[i] & 0xff];
        if ([newHexStr length] == 1) {
            hexStr = [NSString stringWithFormat:@"%@0%@", hexStr, newHexStr];
        } else {
            hexStr = [NSString stringWithFormat:@"%@%@", hexStr, newHexStr];
        }
    }
    return hexStr;
}

DES加密解密

//**************************CBC模式*********************************

/// 需要初始化iv的DES加密。（CBC模式）
+ (NSString *)encodeDesCBCWithString:(NSString*)stringCBC {
    
    NSData*data;
//    NSString*ciphertext =nil;
    NSData *textData = [stringCBC dataUsingEncoding:NSUTF8StringEncoding];
    NSUInteger dataLength = [textData length];
    unsigned char buffer[1024];
    
    memset(buffer,0,sizeof(char));
    size_t numBytesEncrypted = 0;
    CCCryptorStatus cryptStatus = CCCrypt(kCCEncrypt, kCCAlgorithmDES,
                                          kCCOptionPKCS7Padding ,
                                          [kASDESKEY UTF8String],kCCKeySizeDES,
                                          iv,
                                          [textData bytes], dataLength,
                                          buffer,1024,
                                          &numBytesEncrypted);
    
    if(cryptStatus ==kCCSuccess) {
        
        data = [NSData dataWithBytes:buffer length:(NSUInteger)numBytesEncrypted];
    }
    
    NSString *result = [data base64EncodedStringWithOptions:NSDataBase64Encoding64CharacterLineLength];
    
    return result;
    
}

/// 需要初始化iv的DES解密。（CBC模式）
+ (NSString*)decodeDesCBCWithString:(NSString *)stringCBC {
    
    
    NSData*plaindata = nil;
    NSData *cipherdata = [[NSData alloc] initWithBase64EncodedString:stringCBC options:NSDataBase64DecodingIgnoreUnknownCharacters];
    //根据解密数据长度设置输出长度。而不是直接设置1024
    size_t bufferSize = cipherdata.length;
    unsigned char buffer[bufferSize];
    
    
//    NSData*plaindata =nil;
    NSString*plaintext =nil;
    //    NSData *cipherdata = [GTMBase64 decodeString:stringCBC];
//    NSData *cipherdata = [[NSData alloc] initWithBase64EncodedString:stringCBC options:NSDataBase64DecodingIgnoreUnknownCharacters];
//    unsigned char buffer[1024];
    
    memset(buffer,0,sizeof(char));
    size_t numBytesDecrypted = 0;
    CCCryptorStatus cryptStatus = CCCrypt(kCCDecrypt, kCCAlgorithmDES,
                                          kCCOptionPKCS7Padding ,
                                          [kASDESKEY UTF8String],kCCKeySizeDES,
                                          iv,
                                          [cipherdata bytes], [cipherdata length],
                                          buffer,bufferSize,
                                          &numBytesDecrypted);
    
    if (cryptStatus ==kCCSuccess) {
        
        NSData*plaindata = [NSData dataWithBytes:buffer length:(NSUInteger)numBytesDecrypted];
        plaintext = [[NSString alloc]initWithData:plaindata encoding:NSUTF8StringEncoding];
        
    }
    
    return plaintext;
    
}